Local anesthetics Flashcards
The axons of peripheral nerves differ in their
size, structure, speed of conduction, myelination, and sensitivity to the local anesthetic blockade
Conduction velocity is increased by
myelination and a wider axonal diameter
What are the three major classes of peripheral nerves?
A, B & C
In the clinical setting, local anesthetics inhibit peripheral nerves in the following order:
B fibers
C fibers
Small diameter A fibers (delta, gamma)
Large diameter A fibers (alpha, beta)
Regression of blockade occurs in the
opposite order of block onset
What is saltatory conduction?
when myelin insulates the axon and allows the electrical signal to skip along only the uninsulated regions
Conduction velocity is a measure of
how fast an axon transmits the axon potential
What is the function of B fibers?
preganglionic ANS fibers
What is the function of C fibers with a sympathetic subtype?
postganglionic ANS fibers
What is the function of C fibers with a dorsal root subtype?
slow pain
temperature
touch
What is the function of A alpha fibers?
skeletal muscle- motor proprioception
What is the function of A beta fibers?
touch
pressure
What is the function of A gamma fibers
skeletal muscle-tone
What is the function of A delta fibers?
fast pain
temperature
touch
What is Cm?
a unit of measure that quantifies the concentration of local anesthetic that is required to block conduction
minimum effective concentration
Fibers that are more easily blocked have a _________ Cm.
lower
Cm is typically _____________ in nerves with a wider diameter
higher
Cm is reduced by
higher tissue pH or a high frequency of nerve stimulation
Which peripheral nerve fiber type is not myelinated?
C fibers
Local anesthetics can bind to the voltage-gated sodium channel when it is in the:
a. resting and active states
b. resting and inactive states
c. active and inactive states
d. active state only
c. active and inactive state